Document 1gxXRvpy9w8O5Z0XM218VxkKZ

HEATINC VENTILATING AIR CONDITIONING GUIDE 1941 If the ashpit door is closed the air admitted through the ashpit is reduced and increased through the other two intake openings. Methods of control of draft conditions when burning oil or gas are noted in Chapter 9, Automatic Fuel Burning Equipment. CLASSIFICATION OF COALS The complex composition of coal makes it difficult to classify it into clear-cut types. Its chemical composition is some indication but coals having the same chemical analysis may have distinctly different burning characteristics. Users are mainly interested in the available heat per Fig. 4. Correct and Incorrect Methods of Draft Regulation in a Hand-Fired Furnace pound of coal, in the handling and storing properties, and in the burning characteristics. A description of the relationship between the qualities of coals and these characteristics requires considerable space; a treatment applicable to heating boilers is given in Bureau of Mines Bulletin No. 276. The classification of coals by rank involves several of the items indicated in a proximate analysis of the coal. This analysis determines the content of volatile matter, fixed carbon, ash and moisture. The calorific value and sulphur content are often reported with the proximate analysis. Volatile matter is the loss of weight when the coal sample is heated to 1732 F for 7 min. Fixed carbon is the difference from 100 per cent of the sum of other losses, not including sulphur. Ash is the incombustible impurity in the coal and has no heating value. Moisture is the inherent and ex traneous water in the fuel. Other important qualities of. coals are the screen sizes, ash softening temperature, friability, caking tendency, and the qualities of the volatile matter. In considering these factors the following points are of interest. The volatile products given off by coals when they are heated differ materially in the ratios by weight of the gases to the oils and tars. No heavy oils or tars are given off by anthracite, and very small quantities are given off by semi-anthracite. As the volatile matter in the coal increases to as much as 40 per cent of ash and moisture-free coal, in creasing amounts of oils and tars are released. For coals of higher volatile content, the relative quantity of oils and tars decreases, so it CHAPTER 7. COMBUSTION AND FUELS 1 w in the sub-bituminous coals and in lignite. The percentage of ash 1S H'ts fusion temperature do not indicate how the ash is distributed aH how much of it is less fusible lumps of slate or shale. 01A classification of coals is given in Table 5, and a brief description of the ir' ds of fuels is given in the following paragraphs, but it should be lan -ze(j that there are no distinct lines of demarcation between the tods, and that they graduate into each other. Anthracite is a clean, dense, hard coal which creates very little dust in handling. It moaratively hard to ignite but it burns freely when well started. It is non-caking, Is urns uniformly and smokelessly with a short flame, and it requires little attention to 'l^'fuel bed between firings. It is capable of giving a high efficiency in the common ,n*\ of hand-fired furnaces. A tabulation of the quality of the various anthracite sura will be found in Bureau of Mines Report of Investigations No. 3283. Semi-anthracite has a higher volatile content than anthracite. It is not so hard and ignites somewhat more easily; otherwise its properties are similar to those of anthracite. Table 5. Classification of Coals by Rank3 Legend: F.C. = Fixed Carbon. V.M. = Volatile Matter. Btu = British thermal units. Class Group Limits op Fixed Carbon oa Btu Mineral-Matter-Free Basis Requisite Physical Properties I. Anthracite... 1. Meta-anthracite2. Anthracite-------- - 3. Semi-anthracite- %F.C., 98 per cent or more (Dry M., 2 per cent or less) Dry F.C., 92 per cent or more and less than 98 per cent (Dry V.M., 8 per cent or less and more man 2 per cent) Non-agglomerating* Dry F.C., 86 per cent or more and leas than 92 per cent (Dry V.M., 14 per cent or less and more than 8 per cent) 11 Bitumiuous4- 1. Low volatile bituminous coal-- Dry F.C.. 78 per cent or more and less than 86 per cent (Dry V.M. 22 per cent or less and more than 14 per cent) 2. Medium volatile bituminous coal Dry F.C., 69 per cent or more and less than 78 per cent (Dry V.M., 31 per cent or less and more than 22 per cent) 3. High volatile A bituminous coal.l Dnr F.C., less than 69 per cent (Dry V.M., more than 31 per cent); and moist* Btu, 14,000* or more 4. High volatile B bituminous coal. Moist* Btu, 13,000 or more and less than 14.000* 5. High volatile C bituminous coal. Moist Btu. 11,000 or more and tees than 13,000* Esther agglomerating* or non-weathering/ 1. Sub-bituminous A coal______ ill. Sub-bituminous.. 2. Sub-bituminous B coal______ 3. Sub-bituminous C coal______ Moist Btu, 11.000 or more and less than 13,000* Moist Btu, 9500 or more and less Both weathering and than 11,000* non-agglomerating* Moist Btu, 8300 or more and less than 9500* IV. Lignitic... !. Lignite-- 2. Brown coal. Moist Btu less than 8300 Moist Btu less than 8300 Consolidated Unconsolidated This classification does not include a few coals which have unusual physical and chemical properties and which come within the limits of fixed carbon or Btu of the high-volatile bituminous and sub-bituminous ranks. AH of these coals either contain less than 48 per cent dry, mineral-matter-free fixed carbon or have more than 15,500 moist, mineral-matter-free Btu. *If agglomerating, classify in low-volatile group of the bituminous class. *Moi$t Btu refers to coal containing its natural bed moisture but not including visible water on the surface of the coal. 4It is recognized that there may be non-caking varieties in each group of the bituminous class. Coals having 69 per cent or more fixed carbon on the dry, mineral-matter-free basis shall be classified according to fixed carbon, regardless of Btu. /There are three varieties of coal in the High-volatile C bituminous coal group, namely. Variety 1, agglomerating and non-weathering; Variety 2, agglomerating and weathering; Variety 3, non-agglomerating and non-weathering. Adapted from A.S.T.M. Standards, 1937, Supplement, p. 145, American Society for Testing Materials, Philadelphia. 153